Mad cow disease or bovine spongiform encephalopathy (BSE) is a progressive, invariably fatal neurodegenerative disease in cattle. BSE was recognized as a public health concern in 1996 when young Britons were diagnosed with what appeared to be a new form of a familial illness of older age, Creutzfeldt-Jakob Disease (CJD). British scientists linked the development of this “variant Creutzfeldt-Jakob Disease” (vCJD) to exposure to and/or consumption of BSE cattle. As of November 2002, 143 cases of “definite or probable” vCJD had been diagnosed in the UK.
The European Union has created a policy to cull cohorts in herds of cattle in which a BSE marker is detected. Cohorts, which have an approximately 100-fold increased BSE risk, are defined as all animals born and/or raised in the same herd as a confirmed BSE or prion-positive case within twelve months before and after the date of birth of the BSE index case. Cohort culling is most often accomplished through back-tracing from a slaughterhouse detection. Unfortunately, new variant cases of BSE in cattle younger than twenty four months in Japan and France appear to indicate a change in the clinical parameters of BSE (Biacabe, et al. in Int. Conf. of Prion Diseases: From basic Research to intervention concepts. 44Munich; 2003; Casalone, et al. in Int. Conf. of Prion Diseases: From basic Research to intervention concepts. 256Munich; 2003).
Early stage spongiform encephalopathies are difficult to detect by prion testing because prion accumulation is most often associated with late-stage disease. Genetic tests for prion gene polymorphisms are currently used to determine the susceptibility of sheep for scrapie (Hunter, et al. Arch Virol 141:809-824, 1996). No such diversity of prion genes is found in BSE. However, the detection of nucleic acids in cattle sera (Brenig, Schutz, & Urnovitz, Berl Munch Tierarztl Wochenschr 115:122-124, 2002) has previously been reported. Tests for detection and monitoring of genetic material associated with chronic illnesses other than BSE can be performed using sera. Such serum nucleic acids (SNA) associated tests are often designed to detect unique nucleic acid targets, usually of exogenous origin, e.g. HIV-1, CMV, HCV and HBV. SNAs of possible endogenous origin also have been found to be associated with chronic illnesses in humans (Urnovitz, et al. Clin Diagn Lab Immunol 6:330-335, 1999; Durie, Urnovitz, & Murphy Acta Oncol 39:789-796, 2000). However, this approach has not been applied to detection of transmissible spongiform encephlopathies.
It has been suggested that current tests are not sensitive enough to fully protect against the entry of BSE cattle into the human food chain (Knight, Nature 426:216, 2003). Further, current tests cannot identify cohort herd mates of BSE-infected cattle that have an increased risk of BSE. The current invention addresses this need.